Reaction sintered silicon nitride may be prepared in much purer form than the hot pressed material by using high purity silicon powders and nitrogen gas in a solid gas reaction at a relatively low temperature (1300.degree.-1450.degree. C.). Reaction sintered silicon nitride is perhaps the best candidate high temperature structural ceramic for applications requiring moderate strength. Furthermore, the low cost and ease of fabrication to near net shape combined with a low modulus of elasticity and coefficient of thermal expansion, critical parameters for good thermal shock resistance, make reaction sintered nitride a unique ceramic material for use in limited life gas turbine engines, rocket and laser nozzles, and radomes.
The foregoing favorable aspects combine to provide a strong impetus for its application as a high temperature structural ceramic. However, there are two major physical properties, namely, oxidation resistance and room temperature strength, that require improvement. Both of these properties are sensitive to surface and interconnected porosity in the as-nitrided material.
It is a principal object of this invention, therefore, to provide a process for filling or reducing the open pore volume in reaction sintered silicon nitride.
Another object of the invention is to provide a process for increasing the density and improving the room temperature strength of a reaction sintered silicon nitride body.
A further object of the invention is to provide a silicon nitride body infiltrated with a thermally decomposed organosilicon compound.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.